Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.72	7.811%	$56.838	$56.84	$56.85	$56.80
Purchase #2	$60.71	10.273%	$66.9467	$66.95	$66.95	$66.90
Purchase #3	$235.60	4.608%	$246.4564	$246.46	$246.45	$246.50
Purchase #4	$59.99	9.531%	$65.7076	$65.71	$65.70	$65.70
Purchase #5	$199.59	3.335%	$206.2463	$206.25	$206.25	$206.20
Purchase #6	$135.39	3.297%	$139.8538	$139.85	$139.85	$139.90
Purchase #7	$63.31	7.218%	$67.8797	$67.88	$67.90	$67.90
7 purchase totals =	$807.31		$849.9285	$849.94	$849.95	$849.90